All the considerations above motivated the exploration of alternative scenarios, invoked to decrease the BH growth timescale (the \(e-\) folding time, \(t_e\)  defined above) and grow SMBHs by \(z\sim 6-7\) ,
such as the formation of populations of more massive seeds (the heavy channel discussed in Section ), mergers and/or a very rapid/efficient mass growth mechanisms (see, e.g., the recent review by [1]}).
